CHAPTER 38: Anatomy

The anterior abdominal wall provides core support to the human torso, confines abdominal viscera, and contributes muscular action for functions such as respiration and elimination. In gynecology, an understanding of the layered structure of the anterior abdominal wall is needed to effectively enter the peritoneal cavity for surgery without neurovascular complications.

Skin and Subcutaneous Layer

Within the skin, the term Langer lines describes the orientation of dermal fibers. In the anterior abdominal wall, they are arranged primarily transversely (Fig. 38-1). As a result, vertical skin incisions sustain more lateral tension and thus in general, develop wider scars compared with transverse skin incisions.

The subcutaneous layer lies deep to the skin. In the anterior abdominal wall, this layer is separated into a superficial, predominantly fatty layer known as Camper fascia and a deeper, more membranous layer known as Scarpa fascia (Fig. 38-2). Camper and Scarpa fasciae are not discrete layers but represent a continuum. If traced caudally, scarpa fascia is continuous with Colles fascia in the perineum.

Clinically, Scarpa fascia is better developed in the lower abdomen and during surgery can be best identified in the lateral portions of a low transverse incision, just superficial to the rectus fascia. In contrast, this fascia is rarely recognized during midline incisions.

Rectus Sheath

The external oblique, internal oblique, and transversus abdominis muscles (flank muscles) all contain a lateral muscular portion and medial fibrous aponeurotic portion. All of their aponeuroses conjoin, and these layers create the rectus sheath (see Fig. 38-2). In the midline, the aponeurotic layers fuse to create the linea alba. In the lower abdomen, transition from the muscular to the aponeurotic component of the external oblique muscle takes place along a vertical line through the anterior superior iliac spine. Transition from muscle to aponeurosis for the internal oblique and transversus abdominis muscles takes place at a more medial site. Accordingly, during low transverse incisions, muscle fibers of the internal oblique muscle are often noted below the aponeurotic layer of the external oblique muscle.

The anatomy of the rectus sheath above and below the arcuate line has significance (see Fig. 38-2). This horizontal line defines the level at which the rectus sheath passes only anterior to the rectus abdominis muscle, and this line typically lies midway between the umbilicus and pubic symphysis. Cephalad to the arcuate line, the rectus sheath lies both anterior and posterior to the rectus abdominis muscle. At this level, the anterior rectus sheath is formed by the aponeurosis of the external oblique muscle and the split aponeurosis of the internal oblique muscle. The posterior rectus sheath is formed by the split aponeurosis of the internal oblique muscle and aponeurosis of the transversus abdominis muscle. Caudad to the arcuate line, all aponeurotic layers pass anterior to the rectus abdominis muscle. Thus, in the lower abdomen, the posterior surface of the rectus abdominis muscle is in direct contact with the transversalis fascia, described next.

Surgically, because the aponeuroses of the internal oblique and transversus abdominis muscles in the lower abdomen fuse, only two layers are identified during low transverse fascial incisions. In contrast, during midline vertical incision, only one fascial layer, namely, the linea alba, is encountered.

Similar to skin fibers, the flank muscle and rectus sheath fibers are oriented primarily transversely. Thus, suture lines placed in a vertical fascial incision must withstand more tension than those in a transverse incision. As a result, vertical fascial incisions are more prone to dehiscence and hernia formation. In addition to incisional hernias, ventral wall hernias are most common along the linea alba. Another type of anterior abdominal wall hernia, the Spiegelian hernia, is rare and forms at the lateral rectus abdominis border, typically at the level of the arcuate line (Fig. 11-8).

Transversalis Fascia

This thin fibrous tissue layer lies between the inner surface of the transversus abdominis muscle and preperitoneal fat. Thus, it serves as part of the general fascial layer that lines the abdominal cavity (see Fig. 38-2) (Memon, 1999). Inferiorly, the transversalis fascia blends with the periosteum of the pubic bones.

Surgically, this fascia is best recognized as the layer bluntly or sharply dissected off the anterior surface of the bladder during entry into the abdominal cavity. This is the layer of tissue that is last penetrated to gain extraperitoneal entry into the retropubic space.

Peritoneum

The peritoneum that lines the inner surface of the abdominal walls is termed parietal peritoneum. In the anterior abdominal wall, there are five elevations of parietal peritoneum that are raised by different structures (see Fig. 38-2). All five converge toward the umbilicus and are known as umbilical ligaments.

The single median umbilical ligament is formed by the urachus, an obliterated tube that extends from the apex of the bladder to the umbilicus. In fetal life, the urachus, which is a fibrous remnant of the allantois, extends from the umbilical cord to the urogenital sinus, which gives rise to the bladder. The paired medial umbilical ligaments are formed by the obliterated umbilical arteries that connected the internal iliac arteries to the umbilical cord in fetal life. The paired lateral umbilical ligaments contain the patent inferior epigastric vessels. The ­initial course of these vessels is just medial to the round ligament as the ligament enters the deep inguinal ring (Fig. 38-3).

Surgically, transection of a patent urachus can result in extravasation of urine into the abdominal cavity. In addition, the differential diagnosis of a midline anterior abdominal wall cyst includes urachal cyst, urachal sinus, and urachal diverticulum.

The umbilical ligaments serve as valuable laparoscopic landmarks. First, the inferior epigastric vessels can be injured during accessory trocar placement (Hurd, 1994; Rahn, 2010). Thus, direct visualization of the lateral umbilical folds can prevent injury to these vessels during laparoscopic port placement. Second, the medial umbilical ligaments, if followed proximally, can guide a surgeon to the internal iliac artery and then to the uterine arteries. The medial umbilical ligament also forms the medial border of the paravesical space, which is developed during radical hysterectomy to isolate the parametrium.

Blood Supply

Femoral Branches

The superficial epigastric, superficial circumflex iliac, and external pudendal arteries arise from the femoral artery just below the inguinal ligament in the femoral triangle, which is bordered by this ligament, the sartorius muscle, and the adductor longus muscle. These vessels supply the skin and subcutaneous layers of the anterior abdominal wall and mons pubis. The superficial epigastric vessels course diagonally toward the umbilicus, similar to the inferior “deep” epigastric vessels.

Surgically, during low transverse skin incision creation, the superficial epigastric vessels can usually be identified halfway between the skin and the rectus fascia, several centimeters from the midline. During laparoscopic procedures in thin patients, these vessels can be identified by transillumination (Chap. 41).

The external pudendal vessels form rich anastomoses with their contralateral equivalents and with other superficial branches. These anastomoses account for the extensive bleeding often encountered with incisions made in the mons pubis area such as for retropubic midurethral sling incisions.

External Iliac Branches

The inferior “deep” epigastric vessels and deep circumflex iliac vessels are branches of the external iliac vessels (see Fig. 38-3). They supply the muscles and fascia of the anterior abdominal wall. The inferior epigastric vessels initially course lateral to, then posterior to the rectus abdominis muscle, which they supply. They then pass anterior to the posterior rectus sheath and course between the sheath and the rectus muscles (see Figs. 38-2 and 38-3). Near the umbilicus, the inferior epigastric vessels anastomose with the superior epigastric artery and veins, which are branches of the internal thoracic vessels.

Hesselbach triangle is the region in the anterior abdominal wall bounded inferiorly by the inguinal ligament, medially by the lateral border of the rectus muscles, and laterally by the inferior epigastric vessels (Fig. 38-4). Direct hernias protrude through the abdominal wall within Hesselbach triangle. In contrast, indirect hernias protrude into the deep inguinal ring lying lateral to this triangle.

Surgically, low transverse abdominal incisions that extend beyond the lateral margins of the rectus muscles can lead to inferior epigastric vessel laceration with severe hemorrhage or anterior abdominal wall hematoma formation. These vessels should be identified and ligated when performing a Maylard incision. As another surgical landmark, the deep circumflex iliac vein serves as the caudal border during pelvic lymph node dissection.

Innervation

The anterior abdominal wall is innervated by the abdominal extensions of the intercostal nerves (T7-11), the subcostal nerve (T12), and the iliohypogastric and the ilioinguinal nerves (L1) (see Fig. 38-3). The T10 dermatome approximates the level of the umbilicus. Of these, the iliohypogastric nerve provides sensation to the skin over the suprapubic area. The ilioinguinal nerve supplies the skin of the lower abdominal wall and upper portion of the labia majora and medial portion of the thigh through its inguinal branch (see Fig. 38-4). At a site 2 to 3 cm medial to the anterior superior iliac spine, these two nerves pierce through the internal oblique muscle and course superficial to it and toward the midline (Whiteside, 2003).

Clinically, the ilioinguinal and iliohypogastric nerves can be entrapped during closure of low transverse incisions, especially if incisions extend beyond the lateral borders of the rectus abdominis muscle. They may also be wounded by lower abdominal insertion of accessory trocars. The risk of iliohypogastric and ilioinguinal nerve injury can be minimized if lateral trocars are placed superior to the anterior superior iliac spines and if low transverse fascial incisions are not extended beyond the lateral borders of the rectus muscle (Rahn, 2010).

Pelvic Bones and Joints

The sacrum; the coccyx; and two hip bones, termed the innominate bones form the bony pelvis (Fig. 38-5). The innominate bones consist of the ilium, ischium, and pubis, which fuse at the acetabulum, a cup-shaped structure that articulates with the femoral head. The ilium articulates with the sacrum posteriorly at the sacroiliac joint, and the pubic bones articulate with each other anteriorly at the symphysis pubis. The sacroiliac joint is a synovial joint that connects the articular surfaces of the sacrum and ilium. This joint and its ligaments contribute significantly to the stability of the bony pelvis. The symphysis pubis is a cartilaginous joint, which connects the articular surfaces of the pubic bones by way of a fibrocartilaginous disc. The ischial spines are clinically important bony prominences that project posteromedially from the medial surface of the ischium approximately at the level of the fifth sacral vertebra (S5).

Pelvic Openings

The posterior, lateral, and inferior walls of the pelvis have several openings through which many important structures pass. The large obturator foramen between the ischium and pubis is filled almost completely by the obturator membrane. In the superior portion of this membrane, a small aperture known as the obturator canal allows passage of the obturator neurovascular bundle into the medial (adductor) compartment of the thigh (Fig. 38-6).

The posterolateral walls of the pelvis are not covered by bone. Instead, two important accessory ligaments, the sacrospinous and sacrotuberous ligaments, divide the greater and lesser sciatic notches of the ischium into the greater sciatic foramen and lesser sciatic foramen. Through the greater sciatic foramen, the ­piriformis muscle, internal pudendal and superior and inferior gluteal vessels, sciatic and pudendal nerve, and other branches of the sacral nerve plexus pass in close proximity to the ischial spines. Surgically, this anatomy is critical to avoid neurovascular injury during sacrospinous fixation procedures and when administering pudendal nerve blockade (Roshanravan, 2007).

The internal pudendal vessels, pudendal nerve, and obturator internus tendon pass through the lesser sciatic foramen. Posteriorly, four pairs of pelvic sacral foramina allow passage of the anterior divisions of the first four sacral nerves and lateral sacral arteries and veins.

Ligaments

The ligaments of the pelvis vary in composition and function. They range from connective tissue structures that support the bony pelvis and pelvic organs to smooth muscle and loose areolar tissue that add no significant support. The sacrospinous, sacrotuberous, and anterior longitudinal ligaments of the sacrum consist of dense connective tissue that joins bony structures and contributes significantly to bony pelvis stability (see Fig. 38-6).

The round and broad ligaments consist of smooth muscle and loose areolar tissue, respectively. Although they connect the uterus and adnexa to the pelvic walls, they do not contribute to the support of these organs. In contrast, the cardinal and uterosacral ligaments do aid pelvic organ support and are discussed later.

Clinically, the sacrospinous and anterior longitudinal ligament serve as suture fixation sites in suspensory procedures used to correct pelvic organ prolapse. The iliopectineal ligament, also termed Cooper ligament, is a thickening in the pubic bone periosteum, which is often used to anchor sutures in retropubic bladder neck suspension procedures (Fig. 38-7).

The posterior, lateral, and inferior walls of the pelvis are partially covered by striated muscles and their investing layers of fasciae (see Fig. 38-7). The piriformis muscle arises from the anterior and lateral surface of the sacrum and partially fills the posterolateral pelvic walls. It exits the pelvis through the greater sciatic foramen, attaches to the greater trochanter of the femur, and functions as an external or lateral hip rotator. Clinically, stretch injury to the piriformis muscle may cause persistent hip pain that can be confused with other hip or pelvic pathology.

The obturator internus muscle partially fills the sidewalls of the pelvis. This muscle arises from the pelvic surfaces of the ilium and ischium and from the obturator membrane. It exits the pelvis through the lesser sciatic foramen, attaches to the greater trochanter of the femur, and also functions as an external hip rotator.

The fascia that invests striated muscles is termed parietal fascia. Pelvic parietal fascia provides muscle attachment to the bony pelvis and serves as anchoring points for visceral fascia, also termed endopelvic fascia. The arcus tendineus levator ani is a condensation of parietal fascia covering the medial surface of the obturator internus muscle (see Fig. 38-7 and Fig. 38-8). This structure serves as the point of origin for parts of the very important levator ani muscle. Also shown is the arcus tendineus fascia pelvis, a condensation of parietal fascia covering the medial aspects of the obturator internus and levator ani muscles. It serves as the lateral point of attachment of the anterior vaginal wall.

The muscles that span the pelvic floor are collectively known as the pelvic diaphragm (see Figs. 38-7, 38-8, and Fig. 38-9). This diaphragm consists of the levator ani and coccygeus muscles, along with their superior and inferior investing fascial layers. Inferior to the pelvic diaphragm, the perineal membrane and perineal body also contribute to the pelvic floor. The urogenital hiatus is the U-shaped opening in the pelvic floor muscles through which the urethra, vagina, and rectum pass.

Levator Ani Muscles

These are the most important muscles in the pelvic floor and provide critical pelvic organ support (see Figs. 38-7 through 38-9). Physiologically, normal levator ani muscles maintain a constant state of contraction, thus providing a stable floor, which supports the weight of the abdominopelvic contents against intraabdominal forces.

The levator ani muscle is a complex unit, which consists of several muscle components with different origins and insertions and therefore different functions. The pubococcygeus, puborectalis, and iliococcygeus muscles are the three components. Of these, the pubococcygeus muscle is further divided into the pubovaginalis, puboperinealis, and puboanalis muscles according to their fiber attachments. Due to the significant attachments of the pubococcygeus muscle to the walls of the pelvic viscera, the term pubovisceral muscle is frequently used (Kerney, 2004; Lawson, 1974).

Pubococcygeus Muscle

The anterior ends of the pubococcygeus (pubovisceral muscle) arise on either side from the inner surface of the pubic bone. The pubovaginalis refers to the medial fibers that attach to the lateral walls of the vagina (see Fig. 38-9). Although there are no direct attachments of the levator ani muscles to the urethra in females, those fibers of the muscle that attach to the vagina are responsible for elevating the urethra during a pelvic muscle contraction and hence may contribute to urinary continence (DeLancey, 1990). The puboperinealis refers to the fibers that attach to the perineal body and draw this structure toward the pubic symphysis. The puboanalis refers to the fibers that attach to the anus at the intersphincteric groove between the internal and external anal sphincters. These fibers elevate the anus and, along with the rest of the pubococcygeus and puborectalis fibers, keep the urogenital hiatus narrowed (see Fig. 38-8).

Puborectalis Muscle

The puborectalis represents the medial and inferior fibers of the levator ani muscle that arise on either side from the pubic bone and form a U-shaped sling behind the anorectal junction (Figs. 38-8 through 38-10). The action of the puborectalis draws the anorectal junction toward the pubis, contributing to the anorectal angle. This muscle is considered part of the anal sphincter complex and may contribute to fecal continence (Chap. 25).

Iliococcygeus Muscle

This muscle is the most posterior and thinnest part of the levator ani muscle and has a primarily supportive role. It arises laterally from the arcus tendineus levator ani and the ischial spines (see Figs. 38-7 through 38-10). Muscle fibers from one side join those from the opposite side in the midline between the anus and the coccyx. This meeting line is termed the iliococcygeal or anococcygeal raphe. In addition to the iliococcygeus muscle, some fibers of the pubococcygeus muscle pass behind the rectum and attach to the coccyx. These muscle fibers course cephalad or deep to the iliococcygeus muscle and may also contribute to the anococcygeal raphe. The levator plate is the clinical term used to describe the anococcygeal raphe (see Fig. 38-10). This portion of the levator muscles forms a supportive shelf on which the rectum, upper vagina, and uterus rest.

The levator plate in women with normal support has a mean angle of 44 degrees relative to a horizontal reference line during Valsalva, although earlier studies suggested no elevation (Berglas, 1953; Hsu, 2006). During Valsalva, women with prolapse have a statistically greater levator plate angle compared with controls. This larger angle moderately correlates with larger levator hiatus length and greater displacement of the perineal body in women with prolapse compared with controls.

With this in mind, one theory suggests that levator plate support prevents excessive tension or stretching of the connective tissue pelvic ligaments and fasciae (Paramore, 1908). Neuromuscular injury to the levator muscles may lead to eventual sagging or vertical inclination of the levator plate and opening of the urogenital hiatus. Consequently, the vaginal axis becomes more vertical, and the cervix is oriented over the opened hiatus (Fig. 38-11). The mechanical effect of this change is to increase strain on connective tissues that support the pelvic viscera. Increased urogenital hiatus size has been shown to correlate with increased prolapse severity (DeLancey, 1998).

Pelvic Floor Innervation

The pelvic diaphragm muscles are primarily innervated by direct somatic efferents from the second through the fifth sacral nerve roots (S2-5) (see Fig. 38-7) (Barber, 2002; Roshanravan, 2007).

Traditionally, a dual innervation has been described. The pelvic or superior surface of the muscles is supplied by direct efferents from S2-5, collectively known as the nerve to the levator ani muscle. The perineal or inferior surface is supplied by pudendal nerve branches. This latter relationship has been challenged, and investigators suggest that the pudendal nerve does not contribute to levator muscle innervation (Barber, 2002). Pudendal branches do, however, innervate parts of the striated urethral sphincter and external anal sphincter muscles. Such separate innervation may explain why some women develop pelvic organ prolapse and others develop urinary or fecal incontinence (Heit, 1996).

Pelvic Connective Tissue

Subperitoneal perivascular connective tissue and loose areolar tissue are found throughout the pelvis. This tissue connects the pelvic viscera to the pelvic walls and is termed visceral or endopelvic “fascia.” Recall that visceral fascia differs from parietal fascia, which invests most striated muscles (Table 38-1). Visceral fascia is intimately associated with the walls of the viscera and cannot be dissected in the same way that parietal fascia can be separated from its skeletal muscle.

Condensations of visceral connective tissue that have assumed special supportive roles have been given different names. Some examples include the cardinal and uterosacral ligaments and the vesicovaginal and rectovaginal fascia. These are described further in later sections.

The pelvic organs are supplied by the visceral branches of the internal iliac (hypogastric) artery and by direct branches from the abdominal aorta (Fig. 38-12). Clinically, the internal iliac artery can be separated into an anterior and posterior division in the area of the greater sciatic foramen (see Fig. 38-6). Each division has three parietal branches that supply nonvisceral structures. The iliolumbar, lateral sacral, and superior gluteal arteries are the three parietal branches of the posterior division. The internal pudendal, obturator, and inferior gluteal arteries are parietal branches that most commonly arise from the anterior division. The remaining branches of the anterior division supply pelvic viscera (bladder, uterus, vagina, and rectum). These include the uterine, vaginal, and middle rectal arteries and the superior vesical arteries. The superior vesical arteries commonly arise from the patent part of the umbilical arteries (Table 38-2). Internal iliac branches that supply the inferior and middle portions of the bladder are present in women, but their origin is highly variable. The middle rectal arteries are generally very small-caliber vessels but may be absent. They usually contribute to posterior vaginal wall blood supply.

The two most important direct branches of the aorta that contribute to pelvic organ blood supply are the superior rectal and ovarian arteries. The superior rectal artery, which is the terminal branch of the inferior mesenteric artery, anastomoses with the middle rectal arteries, thus contributing blood ­supply to the ­rectum and vagina. The ovarian arteries arise directly from the aorta just inferior to the renal vessels and anastomose with the ascending branch of the uterine artery. These anastomoses contribute to the blood supply of the uterus and adnexa. Other important anastomoses between the aorta and internal iliac arteries include anastomoses between the middle sacral and lateral sacral arteries and anastomoses between the lumbar and iliolumbar arteries.

Nerve supply to the visceral structures in the pelvis (bladder, urethra, vagina, uterus, adnexa, and rectum) arises from the autonomic nervous system. The two most important components of this system in the pelvis include the superior and inferior hypogastric plexuses. The superior hypogastric plexus, also known as the presacral nerve, is an extension of the aortic plexus found below the aortic bifurcation (Fig. 38-13). This plexus primarily contains sympathetic fibers and sensory afferent fibers from the uterus.

The superior hypogastric plexus terminates by dividing into the hypogastric nerves. These nerves join parasympathetic efferents from the second through the fourth sacral nerve roots ­(pelvic splanchnic nerves) to form the inferior hypogastric plexus, also known as the pelvic plexus. In addition, the inferior hypogastric plexus generally receives contributions from the sacral sympathetic trunk.

With variability, fibers of the inferior hypogastric plexus accompany the branches of the internal iliac artery to the pelvic viscera. Accordingly, they are divided into three portions: the vesical, uterovaginal (Frankenhäuser ganglion), and middle rectal plexuses. Extensions of the inferior hypogastric plexus reach the perineum along the vagina and urethra to innervate the clitoris and vestibular bulbs.

Clinically, the sensory afferent fibers contained within the superior hypogastric plexus are targeted in presacral neurectomy, a surgical procedure performed to treat central pelvic pain (Chap. 11). Although visceral and sexual dysfunction has been reported following complete interruption of the superior hypogastric plexus, contributions from the sacral sympathetic trunk may offset interruption of this sympathetic component to the inferior hypogastric plexus. Injury to the branches of the inferior hypogastric plexus during cancer debulking or other extensive pelvic surgeries can lead to varying degrees of voiding, sexual, and defecatory dysfunction.

Uterus

The uterus is a fibromuscular hollow organ situated between the bladder and the rectum. The uterus is divided into two portions: an upper muscular body, the corpus, and a lower fibrous cervix (Fig. 38-14). The transition between the corpus and the cervix is known as the uterine isthmus. This also marks the transition from endocervical canal to endometrial cavity. The portion of the corpus that extends above the entry level of the fallopian tubes into the endometrial cavity is known as the fundus.

The shape, weight, and dimensions of the uterus vary according to parity and estrogen stimulation. Before menarche and after menopause, the corpus and cervix are approximately equal in size, but during the reproductive years, the uterine corpus is significantly larger than the cervix. In the adult, nonpregnant woman, the uterus measures approximately 7 cm in length and 5 cm in width at the fundus.

Endometrium and Serosa

The uterus consists of an inner mucosal layer called the endometrium, which surrounds the endometrial cavity, and a thick muscular wall known as the myometrium. The endometrium consists of columnar epithelium and specialized stroma. The superficial portion of the endometrium undergoes cyclic changes with the menstrual cycle.

The spiral arterioles located in the endometrium undergo hormonally mediated constriction or spasm that promotes shedding of the superficial portion of the endometrium with each menstrual cycle. The deeper basalis layer of the endometrium is preserved after this shedding and is responsible for regeneration of a new superficial layer.

Peritoneal serosa overlies the uterus, except at two sites. First, the anterior portion of the cervix is covered by the bladder. Second, the lateral portions of the corpus and cervix attach to the broad and cardinal ligaments.

Cervix

The uterine cervix begins caudal to the uterine isthmus and is approximately 3 cm in length. The wall of the cervix consists primarily of fibrous tissue and a smaller amount of smooth muscle. The smooth muscle is found on the cervical wall periphery and serves as the attachment point for the cardinal and uterosacral ligaments and for the fibromuscular walls of the vagina.

The attachments of the vaginal walls to the outer cervix divide it into a vaginal part known as the portio vaginalis and a supravaginal part known as the portio supravaginalis (see Fig. 38-14). The portio vaginalis is covered by nonkeratinizing squamous epithelium.

The endocervical canal is lined by columnar, mucus-secreting epithelium. The lower border of the canal, called the external cervical os, contains a transition from the squamous epithelium of the portio vaginalis to the columnar epithelium of the cervical canal. The exact location of this transition, termed the squamocolumnar junction, varies depending on hormonal status (Fig. 29-5). At the upper border of the endocervical canal is the internal cervical os, where the narrow cervical canal becomes continuous with the wider endometrial cavity.

Uterine Support

The main support of the uterus and cervix is provided by the levator ani muscles and the connective tissue that attaches the outer cervix to the pelvic walls. The connective tissue that attaches lateral to the uterus and cervix on each side is called the parametrium and continues caudad along the vagina as the paracolpium. The parametrium consists of what is clinically known as the cardinal ligament and uterosacral ligament (Fig. 38-15).

The cardinal ligaments, also termed transverse cervical ligaments or Mackenrodt ligaments, consist primarily of perivascular connective tissue (Range, 1964). They attach to the posterolateral pelvic walls near the origin of the internal iliac artery and surround the vessels supplying the uterus and vagina.

The uterosacral ligaments insert broadly into the posterior pelvic walls and sacrum and form the lateral boundaries of the cul-de-sac of Douglas. These ligaments originate from the posterior inferior surface of the cervix, but may also originate, in part, from the proximal posterior vagina (Umek, 2004). They consist primarily of smooth muscle and contain some pelvic autonomic nerves (Campbell, 1950; Ripperda, 2015).

Clinically, during pelvic reconstructive surgeries that use the uterosacral ligaments as attachment sites for the vaginal apex, surrounding structures are especially vulnerable (Wieslander, 2007). Namely, the rectum lies medial to the uterosacral ligaments. The ureter, pelvic sidewall vessels, and sacral nerves run lateral to and close to these ligaments.

Round Ligaments

These ligaments are smooth muscle extensions of the uterine corpus and represent the homologue of the gubernaculum testis. The round ligaments arise from the lateral aspect of the corpus just below and anterior to the origin of the fallopian tubes. They extend laterally to the pelvic sidewall (see Fig. 38-14). They enter the retroperitoneal space and pass lateral to the inferior epigastric vessels before entering the inguinal canal through the internal inguinal ring. After coursing through the inguinal canal, the round ligaments exit through the external inguinal ring to terminate in the subcutaneous tissue of the labia majora (see Fig. 38-4). The round ligaments do not significantly contribute to uterine support. They receive their blood supply from a small branch of the uterine or ovarian artery known as Sampson artery.

Clinically, the location of the round ligament anterior to the fallopian tube can assist a surgeon during tubal sterilization through a minilaparotomy incision. This may be especially true if pelvic adhesions limit tubal mobility and thus hinder identification of fimbria prior to tubal ligation.

Division of the round ligament is typically an initial step in abdominal and laparoscopic hysterectomy. Its transection opens the broad ligament leaves and provides access to the pelvic sidewall retroperitoneum. This access allows direct visualization of the ureter and permits isolation of the uterine artery for safe ligation.

Broad Ligaments

These ligaments are double layers of peritoneum that extend from the lateral walls of the uterus to the pelvic walls (see Fig. 38-14). Within the upper portion of these two layers, the fallopian tube, the ovarian ligament, and round ligament are found. Each of these has its separate mesentery, called the mesosalpinx, mesovarium, and mesoteres, respectively, which carry nerves and vessels to these structures. At the lateral border of the fallopian tube and the ovary, the broad ligament ends where the infundibulopelvic ligament, described later on this page, blends with the pelvic wall. The cardinal and distal uterosacral ligaments lie within the lower portion or “base” of the broad ligament.

Uterine Blood Supply

The blood supply to the uterine corpus arises from the ascending branch of the uterine artery and from the medial or uterine branch of the ovarian artery (see Figs. 38-14 and 38-15). The uterine artery may originate directly from the internal iliac artery, or it may have a common origin with the internal pudendal or with the vaginal artery (see Fig. 38-12). The uterine artery approaches the uterus in the area of the uterine isthmus. Here, the uterine artery courses over the ureter and provides a small branch to it. Several uterine veins course along the side of the artery and are variably found over or under the ureter. The uterine artery then divides into a larger ascending and a smaller descending branch that course alongside the uterus and cervix, respectively. These vessels connect on the lateral border of the uterus but form an anastomotic arterial arcade that supplies the uterine walls (Fig. 8-3). The cervix is supplied by the descending or cervical branch of the uterine artery and by ascending branches of the vaginal artery.

Clinically, because the uterus receives dual blood supply from both ovarian and uterine vessels, some surgeons during myomectomy place tourniquets at both the infundibulopelvic ligament and uterine isthmus. This decreases blood flow from the ovarian and uterine arteries, respectively.

Uterine Lymphatic Drainage

Lymphatic drainage of the uterus is primarily to the obturator and internal and external iliac nodes (Fig. 38-16). However, some lymphatic channels from the uterine corpus may pass along the round ligaments to the superficial inguinal nodes, and others may extend along the uterosacral ligaments to the lateral sacral nodes.

Uterine Innervation

The uterus is innervated by fibers of the uterovaginal plexus, also known as Frankenhäuser ganglion. These fibers travel along the uterine arteries and are found in the connective tissue of the cardinal ligaments (see Fig. 38-13).

Ovaries and Fallopian Tubes

Ovaries

The ovaries and fallopian tubes constitute the uterine adnexa. The size and hormonal activity of the ovaries are dependent on age, stage of the menstrual cycle, and exogenous hormonal suppression. During reproductive years, the ovaries measure 2.5 to 5 cm in length, 1.5 to 3 cm in thickness, and 0.7 to 1.5 cm in width.

The ovaries consist of an outer cortex and an inner medulla. The ovarian cortex is made up of a specialized stroma punctuated with follicles, corpora lutea, and corpora albicantia. A single layer of mesothelial cells covers this cortex as a surface epithelium. The medullary portion of the ovary primarily consists of fibromuscular tissue and blood vessels. Vessels and nerves enter the medulla at the hilum, which is a depression along the mesenteric border of the ovary. The medial aspect of the ovary is connected to the uterus by the uteroovarian ligament (see Fig. 38-14). Laterally, each ovary is attached to the pelvic wall by an infundibulopelvic ligament, also termed suspensory ligament of the ovary, which contains the ovarian vessels and nerves.

The blood supply to the ovaries comes from the ovarian arteries, which arise from the anterior surface of the abdominal aorta just below the origin of the renal arteries and from the ovarian branches of the uterine arteries (see Fig. 38-16). The ovarian veins follow the same retroperitoneal course as the arteries. The right ovarian vein drains into the inferior vena cava, and the left ovarian vein drains into the left renal vein.

Lymphatic drainage of the ovaries follows the ovarian vessels to the lower abdominal aorta, where they drain into the paraaortic nodes. For their innervation, the ovaries are supplied by extensions of the renal plexus that course along the ovarian vessels in the infundibulopelvic ligament and variably by contributions of the inferior hypogastric plexus.

Fallopian Tubes

The fallopian tubes are tubular structures that measure 7 to 12 cm in length (see Fig. 38-14). Each tube has four identifiable portions. The interstitial portion passes through the body of the uterus at the region known as the cornua. The isthmic portion begins adjacent to the uterine corpus. It consists of a narrow lumen and a thick muscular wall. The ampullary portion is recognized as the lumen of the isthmic portion of the tube widens. In addition, this segment has a more convoluted mucosa. The fimbriated portion is the distal continuation of the ampullary segment. The fimbriated end has many frondlike projections that provide a wide surface area for ovum pickup. The fimbria ovarica is the extension that contacts the ovary.

The ovarian artery runs along the ovary’s hilum and sends several branches through the mesosalpinx to supply the fallopian tubes (see Fig. 38-14). The venous plexus, lymphatic drainage, and nerve supply of the fallopian tubes follow a similar course to that of the ovaries.

Vagina

The vagina is a hollow viscus whose shape is determined by the structures that surround it and by the attachments of its lateral walls to the pelvic walls. The distal portion of the vagina is constricted by the action of the levator ani muscles (see Fig. 38-10). Above the pelvic floor, the vaginal lumen is more capacious and distensible. In the standing or anatomic position, the apex of the vagina is directed posteriorly toward the ischial spines, and the upper two thirds of the vaginal tube lie almost parallel to the plane of the levator plate. Although variable, the ­average length of the anterior vaginal wall is 7 cm and that of the posterior wall is 9 cm. The recesses within the vaginal lumen in front of and behind the cervix are known as the anterior fornix and posterior fornix, respectively (Fig. 38-17). The vaginal walls consist of three layers: (1) adjacent to the lumen, a layer of nonkeratinized squamous epithelium with an outer lamina propria; (2) a muscular layer of smooth muscle, collagen, and elastin; and (3) an outer adventitial layer of collagen and elastin (Weber, 1995, 1997). These latter two form the fibromuscular component of the vagina.

The vagina lies between the bladder and rectum and, along with its connections to the pelvic walls, provides support to these structures (see Figs. 38-15 and 38-17). The vagina is separated from the bladder anteriorly and the rectum posteriorly by the vaginal adventitia. The lateral continuation of this adventitial layer contributes the paravaginal tissue that attaches the walls of the vagina to the pelvic walls. This paravaginal tissue constitutes the paracolpium. This tissue consists of loose areolar and fatty tissue containing blood vessels, lymphatics, and nerves. The anterior fibromuscular vaginal wall and its paravaginal attachments to the arcus tendineus fascia pelvis represent the layer that supports the bladder and urethra and is clinically referred to as pubovesicocervical fascia (see Fig. 38-15).

The lateral attachments of the posterior vaginal walls are to the fascia covering the upper surface of the levator ani muscles. The posterior vaginal wall and its connective tissue attachments to the sidewall support the rectum. This layer is clinically known as the rectovaginal fascia or fascia of Denonvilliers. However, similar to microscopic findings of the anterior vaginal wall, histologic studies have failed to show a separate layer between the posterior wall of the vagina and the rectum except in the distal 3 to 4 cm. Here, the dense fibromuscular tissue of the perineal body separates these structures (DeLancey, 1999).

Surgically, dissections in the anterior vaginal wall or in the posterior vaginal wall separate portions of the vaginal muscularis from the epithelium for surgeries such as anterior and posterior colporrhaphy. In contrast, posterior or anterior access to the coccygeus-sacrospinous ligament complex is accomplished by incising the full thickness of the anterior or posterior fibromuscular wall of the vagina, respectively. This deeper dissection allows access to the vesicovaginal or rectovaginal space and lateral dissection from these spaces allows access to the pararectal space. Because there is no true histologic “fascial” layer between the vagina and the bladder and between the vagina and the rectum, some recommend that terms such as “pubocervical/pubovesical fascia” or “rectovaginal fascia” be abandoned. They propose that these be replaced by more accurate descriptive terms such as vaginal muscularis or fibromuscular layer of the anterior and posterior vaginal walls.

Vesicocervical and Vesicovaginal “Potential” Spaces

The vesicocervical space begins below the vesicouterine peritoneal fold or reflection, which represents the loose attachments of the peritoneum in the anterior cul-de-sac (see Figs. 38-17 and 38-18). The vesicocervical space continues down as the vesicovaginal space, which extends to the junction of the proximal and middle thirds of the urethra. Below this point, the urethra and vagina fuse.

Clinically, during an abdominal hysterectomy or cesarean delivery, surgeons easily lift and incise the vesicouterine peritoneal fold to create a bladder flap and then open the vesicocervical space. For vaginal hysterectomy, the distance between the anterior vaginal fornix and the anterior cul-de-sac peritoneum spans several centimeters. Thus, to successfully enter the peritoneal cavity anteriorly, proper identification and sharp dissection of the loose connective tissue that lies within the vesicovaginal and then vesicocervical spaces is necessary (see Fig. 38-17) (Balgobin, 2011).

Rectovaginal Space

This is adjacent to the posterior surface of the vagina. It extends from the cul-de-sac of Douglas down to the superior border of the perineal body, which extends 2 to 3 cm cephalad to the hymeneal ring (see Figs. 38-17 and 38-18). Rectal pillars, also known as the deep uterosacral or rectouterine ligaments, are fibers of the cardinal-uterosacral ligament complex that extend down from the cervix and attach to the upper portion of the posterior vaginal wall. These fibers connect the vagina to the lateral walls of the rectum and to the sacrum. These pillars also separate the midline rectovaginal space from the more lateral pararectal spaces.

Clinically, the rectovaginal space contains loose areolar tissue and is easily opened with finger dissection during abdominal surgery (see Fig. 38-18). Perforation of the rectal pillar fibers allows access to the sacrospinous ligaments used in vaginal suspension procedures.

The posterior cul-de-sac peritoneum extends down the posterior vaginal wall 2 to 3 cm inferior to the posterior vaginal fornix (Kuhn, 1982). Thus, during vaginal hysterectomy, in contrast to anterior peritoneal cavity entry, entering the peritoneal cavity posteriorly is readily done by incising the vaginal wall in the area of the posterior fornix (see Fig. 38-17).

Vaginal Support

The main support of the vagina is provided by the levator ani muscles and the connective tissue that attaches the lateral walls of the vagina to the pelvic walls. These attachments are the cardinal and uterosacral ligaments. Although the visceral connective tissue in the pelvis is continuous and interdependent, DeLancey (1992) has described three levels of vaginal connective tissue support that help explain pelvic support dysfunction.

For upper vaginal support, the parametrium continues caudally down the vagina as the paracolpium (see Fig. 38-15). This tissue attaches the upper vagina to the pelvic wall, suspending it over the pelvic floor. These attachments are known as level I support or suspensory axis and provide connective tissue support to the vaginal apex after hysterectomy. In the standing position, level I support fibers are vertically oriented. Clinical manifestations of level I support defects include uterine prolapse or posthysterectomy vaginal vault prolapse.

For midvaginal support, the lateral walls of the vagina’s midportion are attached to the pelvic walls on each side by visceral connective tissue known as endopelvic fascia. These lateral attachments of the vaginal walls blend into the arcus tendineus fascia pelvis and to the medial aspect of the levator ani muscles, and in doing so create the anterior and posterior lateral vaginal sulci (see Fig. 38-15). These grooves run along the vaginal sidewalls and give the vagina an “H” shape when viewed in cross section. As noted earlier, the arcus tendineus fascia pelvis covers the medial aspect of the obturator internus and levator ani muscles. It spans from the inner and lower surface of the pubic bones to the ischial spines (see Figs. 38-7 and 38-15).

Attachment of the anterior vaginal wall to the levator ani muscles is responsible for the bladder neck elevation noted with cough or Valsalva maneuver (see Fig. 38-10). Thus, these midvaginal attachments may have significance for stress urinary continence and are referred to as level II support or the attachment axis. Clinical manifestations of level II support defects include anterior and posterior vaginal wall prolapse and stress urinary incontinence.

For distal vaginal support, the distal third of the vagina is directly attached to its surrounding structures (see Fig. 38-9). Anteriorly, the vagina is fused with the urethra. Laterally it attaches to the pubovaginalis muscle and perineal membrane, and posteriorly to the perineal body. These vaginal attachments are referred to as level III support or the fusion axis and are considered the strongest of the vaginal support components. Clinically, failure of this level of support can result in distal rectoceles or perineal descent. Anal incontinence may also result if the perineal body is absent, as may follow obstetric trauma.

Vaginal Blood Supply, Lymphatics, and Innervation

The main blood supply to the vagina arises from the descending or cervical branch of the uterine artery and from the vaginal artery, a branch of the internal iliac artery (see Fig. 38-12). These vessels form an anastomotic arcade along the lateral sides of the vagina at the level of the vaginal sulci. They also anastomose with the contralateral vessels at points on the anterior and posterior walls of the vagina. Additionally, the middle rectal artery from the internal iliac artery contributes to the posterior vaginal wall supply. The distal walls of the vagina also receive contributions from the internal pudendal artery. Lymphatic drainage of the upper two thirds of the vagina is similar to that of the uterus as described on page 809. The distal part of the vagina drains with the vulvar lymphatics to the inguinal nodes. A more detailed description of the vulvar lymphatics is presented on page 822. Last, vaginal innervation comes from inferior extensions of the uterovaginal plexus, a component of the inferior hypogastric plexus (see Fig. 38-13).

Lower Urinary Tract Structures

Bladder

The bladder is a hollow organ that stores and evacuates urine (Fig. 38-19). Anteriorly, the bladder rests against the inner surface of the pubic bones and then, as it fills, also against the anterior abdominal wall. Posteriorly, it rests against the vagina and cervix. Anteroinferiorly and laterally, the bladder contacts the loose connective and fatty tissue that fills the retropubic space, and here, the bladder lacks a peritoneal covering. The reflection of the bladder onto the abdominal wall is triangular, and the triangle apex is continuous with the median umbilical ligament.

Clinically, an intentional cystotomy can be made to confirm patency of the ureteral orifices, to assist with surgical dissection, or to place ureteral stents. The incision is ideally placed in the retropubic extraperitoneal portion of the bladder close to the apex. This avoids direct contact between the abdominopelvic viscera and the cystotomy site and minimizes the risk of fistula formation.

The bladder wall consists of coarse bundles of smooth muscle known as the detrusor muscle, which extends into the upper part of the urethra. Although separate layers of the detrusor are described, they are not as well defined as the layers of other viscous structures (Fig. 23-1). The innermost layer of the bladder wall is plexiform, which can be seen from the pattern of trabeculations noted during cystoscopy. The mucosa of the bladder consists of transitional epithelium and underlying lamina propria. A submucosal layer intervenes between this mucosa and the detrusor muscle.

The bladder is divided into a dome and a base approximately at the level of the ureteral orifices. The dome is thin walled and distensible, whereas the base is thicker and undergoes less distention during filling (see Fig. 38-15). The bladder base consists of the vesical trigone and the detrusor loops. These loops are two U-shaped bands of fibers found at the vesical neck, where the urethra enters the bladder wall. Ureteral orifices lie within the trigone and empty here into the bladder. The pelvic ureter courses in the pelvic sidewall retroperitoneum and is discussed on page 816.

The blood supply to the bladder arises from the superior vesical arteries, which are branches of the patent portion of the umbilical artery. Other contributors are the middle and inferior vesical arteries, which, when present, often arise from either the internal pudendal or the vaginal arteries (see Fig. 38-12). The nerve supply to the bladder arises from the vesical plexus, a component of the inferior hypogastric plexus (see Fig. 38-13).

Urethra

The female urethra measures 3 to 4 cm in length. The urethral lumen begins at the internal urinary meatus within the bladder, and then courses through the bladder base for less than a centimeter. This region where the urethral lumen traverses the bladder base is called the bladder neck. The distal two thirds of the urethra are fused with the anterior vaginal wall.

The walls of the urethra begin outside the bladder wall. They consist of two layers of smooth muscle, an inner longitudinal and an outer circular, which are in turn surrounded by a circular layer of skeletal muscle referred to as the sphincter urethrae or rhabdosphincter (Fig. 38-20). Approximately at the junction of the middle and lower third of the urethra, and just above or deep to the perineal membrane, two strap skeletal muscles called the urethrovaginal sphincter and compressor urethrae are found. These muscles were previously known as the deep transverse perineal muscles in females. Together with the sphincter urethrae, they constitute the striated urogenital sphincter complex. Together, these three muscles function as a unit and have a complex and controversial innervation. Their fibers act cumulatively to supply constant tonus and to provide emergency reflex activity mainly in the distal half of the urethra to sustain continence.

Distal to the depth of the perineal membrane, the walls of the urethra consist of fibrous tissue, serving as the nozzle that directs the urine stream. The urethra has a prominent submucosal layer that is lined by hormonally sensitive stratified squamous epithelium (Fig. 23-8). Within the submucosal layer on the dorsal (vaginal) surface of the urethra is a group of glands known as the paraurethral glands, which open into the urethral lumen (Fig. 26-3). Duct openings of the two most prominent glands, termed Skene glands, are seen on the inner surface of the external urethral orifice.

The urethra receives its blood supply from branches of the inferior vesical/vaginal and internal pudendal arteries. Although still controversial, the pudendal nerve is believed to innervate the most distal part of the striated urogenital sphincter complex. Somatic efferent branches from S2–S4 that course along the inferior hypogastric plexus variably innervate the sphincter urethrae. An additional discussion of lower urinary tract innervation is found in Chapter 23.

Clinically, chronic infection of the paraurethral glands can lead to urethral diverticula. Due to the multiple openings of these glands along the length of the urethra, diverticula may develop at various sites along the urethra.

Rectum

The rectum is continuous with the sigmoid colon approximately at the level of the third sacral vertebra (see Fig. 38-19). It descends on the anterior surface of the sacrum for approximately 12 cm and ends in the anal canal after passing through the levator hiatus. The anterior and lateral portions of the proximal two thirds of the rectum are covered by peritoneum. The peritoneum is then reflected onto the posterior vaginal wall to form the posterior cul-de-sac of Douglas, also termed rectouterine pouch. In women, the cul-de-sac is located approximately 5 to 6 cm from the anal orifice and can be palpated manually during rectal or vaginal examination. At its commencement, the rectal wall is similar to that of the sigmoid, but near its termination it becomes dilated to form the rectal ampulla, which begins below the posterior cul-de-sac peritoneum.

The rectum contains several, usually three, transverse folds called the plicae transversales recti, also termed valves of Houston (Fig. 38-21). The largest and most constant of these folds is located anteriorly and to the right, approximately 8 cm from the anal orifice. These folds may contribute to fecal continence by supporting fecal matter above the anal canal. Clinically, in the empty state, the transverse rectal folds overlap each other, making it difficult at times to manipulate an examining finger or endoscopy tube past this level.

Pelvic Sidewall

Several retroperitoneal spaces are important for the pelvic surgeon. Of these, the retroperitoneal space of the pelvic sidewalls contains the internal iliac vessels and pelvic lymphatics, pelvic ureter, and obturator nerve.

During surgery, entering the retroperitoneum at the pelvic sidewall can be used to identify the ureter (Fig. 38-22). Moreover, it is an essential step for many of the surgeries described in gynecologic oncology.

Vessels

The major pelvic vessels are shown in Figures 38-12, 38-14, and 38-22. The internal iliac and external iliac vessels and their corresponding lymph node groups lie within the pelvic sidewall retroperitoneal space (see Fig. 38-16).

Clinically, if severe hemorrhage is encountered during pelvic surgery, the internal iliac artery may be ligated to decrease the pulse pressure to pelvic organs. When this vessel is dissected, the ureter is also identified and avoided. The internal iliac artery is ligated distal to the origin of its posterior division branches. This helps to prevent significant devascularization of the gluteal muscles. These posterior division branches generally arise from the posterolateral wall of the internal iliac artery at a site 3 to 4 cm from its origin off the common iliac artery (Bleich, 2007).

Pelvic Ureter

As the ureter enters the pelvis, it crosses over the bifurcation of the common iliac artery or the proximal portion of the external iliac artery and passes just medial to the ovarian vessels (see Fig. 38-15). It descends into the pelvis attached to the medial leaf of the pelvic sidewall peritoneum. Along this course, the ureter lies medial to the internal iliac branches and anterolateral to the uterosacral ligaments (see Figs. 38-14, 38-15, and 38-22). The ureter then traverses through the cardinal ligament approximately 1 to 2 cm lateral to the cervix. Near the level of the uterine isthmus, it courses below the uterine artery (“water under the bridge”). It then travels anteromedially toward the bladder base (see Fig. 38-15). In this path, it runs close to the upper third of the anterior vaginal wall (Rahn, 2007). Finally, the ureter enters the bladder and travels obliquely for approximately 1.5 cm before opening at the ureteral orifices.

The pelvic ureter receives blood supply from the vessels it passes: the common iliac, internal iliac, uterine, and superior vesical vessels. The ureter’s course runs medial to these vessels, and thus its blood supply reaches the ureter from lateral sources. This is important during ureteral isolation. In contrast, the abdominal part of the ureter courses lateral to major vessels and accordingly, it receives most of its blood supply from medially located vessels. Vascular anastomoses on the connective tissue sheath enveloping the ureter form a longitudinal network of vessels.

Clinically, because of the pelvic ureter’s proximity to many structures encountered during gynecologic surgery, emphasis is placed on its precise intraoperative identification. Most ureters are injured during gynecologic surgery for benign disease. More than 50 percent of these injuries are not diagnosed intraoperatively (Ibeanu, 2009). The most common sites of injury include: (1) the pelvic brim area during infundibulopelvic ligament clamping; (2) the isthmic region during uterine artery ligation, (3) the pelvic sidewall during uterosacral ligament suturing, and (4) the lateral vaginal apex during vaginal cuff clamping or suturing.

Presacral Space

This retroperitoneal space lies between the rectosigmoid/posterior abdominal wall peritoneum and the sacrum (Figs. 38-18 and 38-23). It begins below the aortic bifurcation and extends inferiorly to the pelvic floor. Laterally, this space is bounded by the internal iliac vessels and branches and by the fascia that covers the piriformis muscle and sacral nerves. Contained within the loose areolar and connective tissue of this space are the superior hypogastric plexus, hypogastric nerves, and portions of the inferior hypogastric plexus (see Figs. 38-14 and 38-23). The sacral lymph node group is also found here (see Fig. 38-16). In addition, the sacral sympathetic trunk, a continuation of the lumbar trunk, lies against the sacrum’s ventral surface and medial to the sacral foramina.

The presacral space contains an extensive and intricate venous plexus, termed the sacral venous plexus. This plexus is formed primarily by the anastomoses of the middle and lateral sacral veins on the anterior surface of the sacrum. The middle sacral vein commonly drains from this plexus into the left common iliac vein, whereas each lateral sacral vein opens into its respective internal iliac vein. Ultimately, these vessels drain into the caval system. The sacral venous plexus also receives contributions from the lumbar veins of the posterior abdominal wall and from the basivertebral veins that pass through the pelvic sacral foramina. The middle sacral artery, which courses in proximity to the middle sacral vein, arises from the posterior and distal part of the abdominal aorta.

In studies of presacral space vascular anatomy, the left common iliac vein was the closest major vessel identified both cephalad and lateral to the midsacral promontory. The average distance of the left common iliac vein from the midsacral promontory is 2.7 cm (range 0.9–5.2 cm) (Good, 2013b; Wieslander, 2006).

Surgically, the presacral space is most commonly entered to perform abdominal sacrocolpopexy or presacral neurectomy. Importantly, during these procedures, bleeding from the sacral venous plexus may be difficult to control as the veins may retract into the sacral foramina. For sacrocolpopexy, the sacral promontory’s midpoint is an important landmark, and the right ureter, right common iliac artery, and left common iliac vein are found within 3 cm of the midsacral promontory (Good, 2013b; Weislander, 2007). Moreover, the first sacral nerve can be expected approximately 3 cm from the upper surface of the sacrum and 1.5 cm from the midline (Good, 2013b). In supine women, the most prominent presacral space structure is the L5–S1 disc, which extends approximately 1.5 cm cephalad to the “true” sacral promontory (Good, 2013a). Awareness of a 60-degree average drop between the anterior surfaces of L5 and S1 vertebrae assists intraoperative localization of the promontory.

Prevesical Space

This space is also called the retropubic space or space of Retzius. During laparotomy, if an extraperitoneal approach is selected, this space can be entered by perforating the transversalis fascial layer of the anterior abdominal wall (see Fig. 38-19). If an intraperitoneal approach is chosen, then only the anterior abdominal wall peritoneum is incised to access this space. The prevesical space is bounded by the bony pelvis and muscles of the pelvic wall anteriorly and laterally and by the anterior abdominal wall ventrally (see Figs. 38-18, 38-19, and Fig. 38-24). The bladder and proximal urethra lie posterior within this space. Attachments of the paravaginal connective tissue to the arcus tendineus fascia pelvis constitute the posterolateral limit of the space and separate this space from the vesicovaginal and vesicocervical spaces.

There are several vessels and nerves in this space. The dorsal vein of the clitoris passes under the lower border of the pubic symphysis and drains into the periurethral-perivesical venous plexus, also termed the plexus of Santorini (Pathi, 2009). The obturator neurovascular bundle courses along the lateral pelvic walls and enters the obturator canal to reach the medial compartment of the thigh. The autonomic nerve branches that supply the bladder and urethra course on the lateral borders of these structures. Additionally, in most women, accessory obturator vessels that arise from or open into the inferior epigastric or external iliac vessels are found crossing the superior pubic rami and connecting with the obturator vessels near the obturator canal. Clinically, the obliterated umbilical or the superior vesical arteries are used to describe the medial boundary of the paravesical space. The paravesical space represents the lateral boundaries of the prevesical space (see Fig. 38-18).

Surgically, injury to the obturator neurovascular bundle or accessory obturator vessels is most often associated with pelvic lymph node dissection, paravaginal defect repair, and pelvic fractures. The obturator canal is found approximately 5 to 6 cm from the midline of the pubic symphysis, and 1 to 2 cm below the upper margin of the iliopectineal ligament (Drewes, 2005).

Bleeding from the periurethral-perivesical venous plexus is often encountered while placing sutures or passing needles into this space during retropubic bladder neck suspensions and midurethral retropubic procedures, respectively. This venous ooze usually stops when pressure is applied or sutures are tied.

In a cadaver study, proximal paravaginal defect repair sutures placed at the level of the ischial spines were found an average of 2.3 cm away from the ureter but as close as 5 mm (Rahn, 2007). This further highlights the value of intraoperative cystoscopy during retropubic surgeries.

Vulva

The external female genitalia, collectively known as the vulva, lie on the pubic bones and extend posteriorly. Structures included are the mons pubis, labia majora and minora, clitoris, vestibule, vestibular bulbs, greater vestibular glands (Bartholin glands), lesser vestibular glands, Skene and paraurethral glands, and the urethral and vaginal orifices (Fig. 38-25). The embryologic development and homologues of these structures can be found in Table 18-1.

Mons Pubis and Labia Majora

The mons pubis, also called the mons veneris, is the rounded fat pad that lies ventral to the pubic symphysis. The labia majora are two prominent folds that extend from the mons pubis toward the perineal body posteriorly. Skin over the mons pubis and labia majora contains hair and has a subcutaneous layer similar to that of the anterior abdominal wall. The subcutaneous layer consists of a superficial fatty layer similar to Camper fascia, and a deeper membranous layer, Colles fascia (see Fig. 38-25). Also known as the superficial perineal fascia, Colles fascia is similar to and continuous with Scarpa fascia of the anterior abdominal wall.

The round ligament and obliterated processus vaginalis, which is also termed the canal of Nuck, exit the inguinal canal and attach to the adipose tissue or skin of the labia majora.

Clinically, Colles fascia attaches firmly to the ischiopubic rami laterally and the perineal membrane posteriorly. These attachments prevent the spread of fluid, blood, or infection from the superficial perineal space to the thighs or posterior perineal triangle. Anteriorly, Colles fascia has no attachments to the pubic rami, and it is therefore continuous with the lower anterior abdominal wall (see Fig. 38-25). This continuity may allow the spread of fluid, blood, and infection between these compartments.

Clinically, a mass found in one labium majus may be a leiomyoma arising from the distal round ligament, a persistent processus vaginalis, or breast tissue along the distal milk line. An indirect inguinal hernia may also reach the labium majus by passing through the deep inguinal ring and inguinal canal.

Labia Minora

These two cutaneous folds lie between the labia majora (see Fig. 38-25). Anteriorly, each labium minus bifurcates to form two folds that surround the glans of the clitoris. The prepuce is the anterior fold that overlies the glans, and the frenulum is the fold that passes below the clitoris. Posteriorly, the labia minora end at the fourchette.

In contrast to the skin that overlies the labia majora, the skin of the labia minora does not contain hair. Also, the subcutaneous tissue is devoid of fat and consists primarily of loose connective tissue. This latter attribute allows mobility of the skin during sex and accounts for the ease of dissection with vulvectomy.

Clinically, labia minora are typically symmetric, but their size and shape can vary widely between women. In some, these winglike structures are pendulous and can be drawn into the vagina during coitus. If associated with dyspareunia in this setting, the labia can be surgically reduced. Moreover, chronic dermatologic diseases such as lichen sclerosus may lead to significant atrophy or disappearance of the labia minora.

Clitoris

This is the female erectile structure homologous to the penis. It consists of a glans, a body, and two crura. The glans contains many nerve endings and is covered by a thinly keratinized stratified squamous epithelium. The body measures approximately 2 cm and is connected to the pubic ramus by the crura (Fig. 38-26).

Vaginal Vestibule

This is the area between the two labia minora. It is bounded laterally by the line of Hart and medially by the hymeneal ring. Hart line represents the demarcation between the skin and mucous membrane on the inner surface of the labia minora. The vestibule extends from the clitoris anteriorly to the fourchette posteriorly (see Fig. 38-25 inset). It contains the openings of the urethra; vagina; greater vestibular glands, also known as Bartholin glands; and Skene glands, which are the largest pair of paraurethral glands. It also contains the numerous openings of the lesser vestibular glands. A shallow vestibular depression known as the navicular fossa lies between the vaginal orifice and the fourchette.

Clinically, localized vulvar dysesthesia—also termed vulvar vestibulitis—is characterized by pain with vaginal penetration, localized point tenderness, and erythema of the vestibular mucosa. In other women, when choosing incision sites for Bartholin gland drainage or marsupialization, Hart line is clinically relevant. That is, in attempts to recreate near-normal gland duct anatomy following these procedures, incisions placed external to Hart line are avoided (Kaufman, 1994).

Vestibular Bulbs

These are homologues to the male penile bulb and corpus spongiosum. They are two elongated, approximately 3-cm long, richly vascular erectile masses that surround the vaginal orifice (see Fig. 38-26). Their posterior ends are in contact with the Bartholin glands. Their anterior ends are joined to one another and to the clitoris. Their deep surfaces are in contact with the perineal membrane, and their superficial surfaces are partially covered by the bulbospongiosus muscles.

Clinically, the proximity of the Bartholin glands to the vestibular bulbs accounts for the significant bleeding often encountered with Bartholin gland excision (Section 43-20). Following vulvar trauma, laceration of these bulbs or the clitoral crus may lead to sizable hematomas.

Bartholin Glands

These are the homologues of the male bulbourethral or Cowper glands. They are in contact with and often overlapped by the posterior ends of the vestibular bulbs (see Fig. 38-26). Each gland is connected to the vestibule by an approximately 2-cm long duct. The ducts open in the groove between the hymen and the labia minora—the vestibule—at approximately 5 and 7 o’clock positions.

The glands contain columnar cells that secrete clear or whitish mucus with lubricant properties. These glands are stimulated by sexual arousal. Contraction of the bulbospongiosus muscle, which covers the superficial surface of the gland, expresses gland secretions.

Clinically, obstruction of the Bartholin ducts by proteinaceous material or by inflammation from infection can lead to cysts of variable sizes. An infected cyst can lead to an abscess, which typically requires surgical drainage. Symptomatic or recurrent cysts may require marsupialization or gland excision.

Perineum

The perineum is the diamond-shaped area between the thighs (see Fig. 38-25). It is bounded deeply by the inferior fascia of the pelvic diaphragm and superficially by the skin between the thighs. The anterior, posterior, and lateral boundaries of the perineum are the same as those of the bony pelvic outlet: the pubic symphysis anteriorly, ischiopubic rami and ischial tuberosities anterolaterally, coccyx posteriorly, and sacrotuberous ligaments posterolaterally. An arbitrary line joining the ischial tuberosities divides the perineum into the anterior or urogenital triangle, and a posterior or anal triangle.

Anterior (Urogenital) Triangle

Structures that comprise the vulva or external female genitalia lie in the anterior triangle of the perineum. The base or posterior border of this triangle is the interischial line, which usually overlies the superficial transverse perineal muscles (see Fig. 38-26).

The anterior perineal triangle can be further divided into a superficial and a deep pouch or space by the perineal membrane. The superficial perineal space lies superficial to the perineal membrane, and the deep space lies above or deep to the membrane.

Superficial Space

This space of the anterior triangle is an enclosed compartment that lies between Colles fascia and the perineal membrane. It contains the ischiocavernosus, bulbo­spongiosus, and superficial transverse perineal muscles; Bartholin glands; vestibular bulbs; clitoris; and branches of the pudendal vessels and nerve. The urethra and vagina traverse this space.

The ischiocavernosus muscle attaches to the medial aspect of the ischial tuberosities posteriorly and the ischiopubic rami laterally. Anteriorly, it attaches to the crus of the clitoris. This muscle may help maintain clitoral erection by compressing the crus of the clitoris, thus retarding venous drainage.

The bulbospongiosus muscle, also known as the bulbocavernosus muscle, covers the superficial portion of the vestibular bulbs and Bartholin glands. These muscles attach to the body of the clitoris anteriorly and the perineal body posteriorly. The muscles act to constrict the vaginal lumen, contributing to the release of Bartholin gland secretions. They may also contribute to clitoral erection by compressing the deep dorsal vein of the clitoris. The bulbospongiosus muscle, along with the ischiocavernosus muscle, acts to pull the clitoris downward.

The superficial transverse perineal muscles are narrow strips that attach to the ischial tuberosity laterally and the perineal body medially. They may be attenuated or even absent, but when present, they contribute to the perineal body.

Deep Perineal Space

This pouch lies deep or superior to the perineal membrane (Fig. 38-27). In contrast to the superficial space, which is a closed compartment, the deep space is continuous superiorly with the pelvic cavity. It contains the compressor urethrae and urethrovaginal sphincter muscles, parts of the urethra and vagina, branches of the internal pudendal artery, and the dorsal nerve and vein of the clitoris.

Perineal Membrane (Urogenital Diaphragm)

Traditionally, a trilaminar, triangular urogenital diaphragm has been described as the main component of the deep perineal space. According to this concept, the urogenital diaphragm consisted of the deep transverse perineal muscles and sphincter urethrae muscles between the perineal membrane (inferior fascia of the urogenital diaphragm) and a superior layer of fascia (superior fascia of the urogenital diaphragm). However, the term diaphragm is used to describe a closed compartment. As described earlier, the deep perineal space is an open compartment. It is bounded inferiorly by the perineal membrane and extends up into the pelvis (Oelrich, 1980, 1983). As a result, when describing perineal anatomy, the terms urogenital diaphragm or inferior fascia of the urogenital diaphragm are misnomers and have been replaced by the anatomically correct term, perineal membrane.

The perineal membrane constitutes the deep boundary of the superficial perineal space (see Fig. 38-27). It attaches laterally to the ischiopubic rami, medially to the distal third of the urethra and vagina, and posteriorly to the perineal body. Anteriorly, it attaches to the arcuate ligament of the pubis. In this area, the perineal membrane is particularly thick and is often referred to as the pubourethral ligament.

The perineal membrane consists of two histologically and probably functionally distinct portions that span the opening of the anterior pelvic triangle (Stein, 2008). The dorsal or posterior portion is a dense fibrous tissue sheet that attaches laterally to the ischiopubic rami and medially to the distal third of the vagina and to the perineal body (see Fig. 38-27). The ventral or anterior portion of the perineal membrane is intimately associated with the compressor urethrae and urethrovaginal sphincter muscles, previously called the deep transverse perineal muscles in the female (see Fig. 38-27 inset). Moreover, the ventral portion of the perineal membrane is continuous with the insertion of the arcus tendineus fascia pelvis to the pubic bones (see Fig. 38-20). The deep or superior surface of the perineal membrane appears to have direct connections to the levator ani muscles, and the superficial or inferior surface of the membrane fuses with the vestibular bulb and clitoral crus.

Clinically, the perineal membrane attaches to the lateral walls of the vagina approximately at level of the hymen. It provides support to the distal vagina and urethra by attaching these structures to the bony pelvis. In addition, its attachments to the levator ani muscles suggest that the perineal membrane may play an active role in support.

Posterior (Anal) Triangle

This triangle contains the ischioanal fossa, anal canal, anal sphincter complex, and branches of the internal pudendal vessels and pudendal nerve (Figs. 38-21, 38-27, and Fig. 38-28). It is bounded deeply by the fascia overlying the inferior surface of the levator ani muscles, and laterally by the fascia overlying the medial surface of the obturator internus muscles. A splitting of the obturator internus fascia in this area is known as the pudendal or Alcock canal (see Figs. 38-6 and 38-21). This canal allows passage of the internal pudendal vessels and pudendal nerve before these structures split into terminal branches to supply the structures of the vulva and perineum (see Fig. 38-28).

The ischioanal or ischiorectal fossa fills most of the anal triangle (see Figs. 38-21 and 38-28). It contains adipose tissue and occasional blood vessels. The anal canal and anal sphincter complex lie in the center of this fossa. The ischioanal fossa is bounded superomedially by the inferior fascia of the levator muscles; anterolaterally by the fascia covering the medial surface of the obturator internus muscles and the ischial tuberosities; and posterolaterally by the lower border of the gluteus maximus muscles and sacrotuberous ligaments. At a superficial level, the ischioanal fossa is bounded anteriorly by the superficial transverse perineal muscles. At a superior or deeper level, there is no fascial boundary between the fossa and the tissues deep to the perineal membrane. Posterior to the anus, the contents of the fossa are continuous across the midline except for the attachments of the external anal sphincter fibers to the coccyx. This continuity of the ischioanal fossa across perineal compartments allows fluid, infection, and malignancy to spread from one side of the anal canal to the other, and also into the anterior perineal compartment deep to the perineal membrane.

The anal sphincter complex consists of two sphincters and the puborectalis muscle. The external anal sphincter consists of striated muscle that surrounds the distal anal canal. It consists of a superficial and a deep portion. The more superficial fibers lie caudal to the internal sphincter and are separated from the anal epithelium only by submucosa. The deep fibers blend with the lowest fibers of the puborectalis muscle. The external sphincter is primarily innervated by the inferior rectal branch of the pudendal nerve. The external anal sphincter is responsible for the squeeze pressure of the anal canal.

The internal anal sphincter is the thickening of the circular smooth muscle layer of the anal wall (see Fig. 38-21). It is under the control of the autonomic nervous system and is responsible for approximately 80 percent of the resting pressure of the anal canal.

As noted earlier, the puborectalis muscle comprises the medial portion of the levator ani muscle that arises on either side from the inner surface of the pubic bones. It passes behind the rectum and forms a sling behind the anorectal junction, contributing to the anorectal angle and possibly to fecal continence (see Figs. 38-9, 38-10, and 38-27).

Perineal Body

This fibromuscular tissue mass lies between the distal part of the posterior vaginal wall and the anus. It is formed by the attachment of several structures. Inferiorly or superficially, the structures that attach to and contribute to the perineal body include the bulbospongiosus, superficial transverse perineal, and external anal sphincter muscles (see Fig. 38-26). Structures that attach at a superior or deeper level are the perineal membrane, levator ani muscles and covering fascia, urethrovaginal sphincter muscles, and distal part of the posterior vaginal wall (see Fig. 38-27). The anterior-to-posterior and the superior-to-inferior extents of the perineal body each measure approximately 2 to 4 cm (see Fig. 38-17).

Clinically, during vaginal laceration repairs and with pelvic reconstructive procedures, particular attention is given to perineal body reconstruction. As noted on page 812, the distal support provided by the perineal body helps prevent pelvic organ prolapse and other pelvic floor dysfunction.

Blood Supply, Lymphatics, and Innervation

Blood Vessels

The external pudendal artery is a branch of the femoral artery and supplies the skin and subcutaneous tissue of the mons pubis (see Fig. 38-3). The internal pudendal artery is a terminal branch of the internal iliac artery (see Fig. 38-6). It exits the pelvis through the greater sciatic foramen, passes behind the ischial spines, and reenters the perineum through the lesser sciatic foramen. It then has a variable course through the pudendal or Alcock canal, and then divides into terminal branches. These are the inferior ­­rectal, perineal, and clitoral arteries (see Fig. 38-28). Branches to the perineum sometimes arise from the pudendal artery before it exits the pelvis. These vessels are called accessory pudendal arteries. Other accessory vessels may also arise directly from the anterior or posterior division of the internal iliac artery.

The veins that drain the structures of the vulva and perineum have courses and names similar to those of the arteries. Venous blood from the vestibular bulbs and other structures, with the exception of the erectile tissue of the clitoris, drains into the internal pudendal veins. The erectile tissue drains into the dorsal vein of the clitoris (see Fig. 38-27). This vein courses backward into the pelvis and terminates in the periurethral–perivesical venous plexus (see Fig. 38-24). The venous plexus that drains the rectum and anal canal empties into the superior, middle, and inferior rectal veins. The superior rectal vein drains into the inferior mesenteric vein, a tributary of the portal vein. The middle rectal vein drains into the internal iliac vein. The inferior rectal vein drains into the internal pudendal and then the internal iliac vein.

Lymphatic Drainage

Structures of the vulva and perineum drain into the inguinal lymph nodes, which are located below the inguinal ligament in the upper anterior and medial thigh (Fig. 38-29). There are 10 to 20 inguinal nodes, which are divided into a superficial and a deep group. Nodes of the superficial inguinal group are more numerous, and they are found in the membranous layer of the subcutaneous tissue of the anterior thigh, just superficial to the fascia lata.

The deep inguinal nodes vary from one to three in number and are located deep to the fascia lata in the femoral triangle. This triangle is bordered superiorly by the inguinal ligament, laterally by the medial border of the sartorius muscle, and medially by the medial border of the adductor longus muscle. The iliopsoas and pectineus muscles form its floor. From lateral to medial, the structures found in this triangle are the femoral nerve, artery, vein, and deep inguinal lymphatics. The femoral canal is the space that lies on the medial side of the femoral vein and that contains the deep inguinal nodes. The femoral ring is the abdominal opening of the femoral canal. The fossa ovalis or saphenous opening is an oval opening in the fascia lata and allows communication between superficial and deep inguinal nodes. Of the deep inguinal nodes, the highest one—Cloquet node—is located in the lateral part of the femoral ring. Efferent channels from the deep inguinal nodes pass through the femoral canal and femoral ring to the external iliac nodes. Lymphatics from the skin of the labia, clitoris, and remainder of the perineum drain into the superficial inguinal nodes. The glans and corpora cavernosa of the clitoris may drain directly to the deep inguinal nodes.

Surgically, sampling of the superficial, and sometimes also the deep, inguinal nodes is completed as one part of radical vulvectomy. Familiarity with the surrounding anatomy is essential.

Innervation

The inferior anal, perineal, and dorsal nerve of the clitoris are branches of the pudendal nerve and provide sensory and motor innervation to the perineum (see Fig. 38-28). The pudendal nerve is a branch of the sacral plexus and is formed by the anterior rami of the second through the fourth sacral nerves (see Fig. 38-6). It has a course and distribution similar to those of the internal pudendal artery. In addition, the perineal branches of the posterior femoral cutaneous nerve (S1-S3) supply the skin of the external genitalia and adjacent proximal medial surface of the thigh.

Clinically, pudendal nerve blocks can be performed transvaginally or transgluteally by injecting local anesthesia just medial and inferior to the ischial spine. Importantly, inadvertent injection of local anesthetic into the internal pudendal vessels may lead to seizure activity and other complications (Chap. 40).

Postsurgical pain in the distribution of the dorsal nerve of the clitoris has been reported following midurethral sling procedures. However, anatomic studies show that this nerve courses superficial or caudal to the perineal membrane, and trocar and mesh placement during these procedures remains deep or cephalad to the membrane (Montoya, 2011; Rahn, 2006).

Clitoral erection requires parasympathetic visceral efferents derived from the pelvic plexus nerves, sometimes called nervi erigentes. These arise from the second to the fourth sacral spinal cord segments. They reach the perineum along the urethra and vagina, passing through the urogenital hiatus (see Fig. 38-13). Sympathetic fibers reach the perineum with the pudendal nerve.